A. Technical Field
Provided is a carbon dioxide extraction apparatus for subcritical and supercritical extractions which may optionally use filter membranes for isolating compounds during carbon dioxide extraction.
B. Description of Related Art
Supercritical CO2 extraction was originally developed by Germany in the 1930's to extract oil from shale for the war effort of World War II. After the conflict ended, it was shown that the same process could be used for extracting flavoring oils from hops for the German beer industry. To this day, the largest CO2 extractors are used for making hops oils for beer.
CO2 extraction generally operates in the following manner. First, plant or other organic or raw materials are inserted into a vessel which operates as an extractor. Next, CO2 gas is pumped from a CO2 tank through a conduit to the extractor. The extractor is pressurized and maintained at a certain temperature so that CO2 gas is compressed to a liquid or supercritical fluid upon its entry into the extractor. In certain cases, the exterior of the extractor may be insulated with an insulation jacket to assist in maintaining the temperature within the extractor. As the liquefied CO2 passes through the plant or other organic or raw material within the extractor, it acts as a solvent, removing (i.e., extracting) various oils and compounds from the plant or other raw materials. The liquefied CO2 containing the extracted oils and compounds is then transferred or pumped to a separator. The separator is maintained at a different temperature and pressure than the extractor which results in the separation of the oil and other extracted compounds from the liquefied CO2 and the conversion of liquefied CO2 into CO2 gas. For example, in certain cases, the extractor is maintained at a pressure of about 1000 psi and the separator is maintained at a pressure of about 200 to about 400 psi to enable the extraction process to be carried out. After entering the separator, oil and other extracted compounds separate from the liquefied CO2 and fall into a collection vessel at the bottom of the separator while the CO2 gas is transferred or pumped through a conduit to either the CO2 tank or to the extractor to be recirculated through the system.
The advantages of CO2 extraction include its ability to be tuned for different extraction parameters by adjusting temperature and pressure and the fact that it leaves no toxic solvent residues within the final product. The disadvantages of CO2 extraction are that it is a complicated process which involves a lot of technical hurdles including the pumping of fluids and achieving and maintaining the specific pressure and temperature swings of fluids and materials involved in the process. Another drawback of CO2 extraction has been the fact that a lot of the monoterpenes or flavor and fragrance oils are lost in the process because they remain volatile and stay entrained in the CO2 vapor rather than falling out into the separators during extraction. These issues have been resolved by Applicant by the development of a method for CO2 extraction which involves no pump and wherein the entire process may be completed within one vessel. This drastically reduces the complexity, costs, and technical problems that CO2 extraction has always been known for. To accomplish the extraction process within a single vessel, a reflux distiller can be incorporated into the system between the separator and the condensing system to cool the CO2 vapor coming from the separator enough to drop out the light oils but not enough to liquefy the CO2.
Moreover, despite the fact that the technology for CO2 extraction has a wide range of applications, an additional obstacle exists in that its use has been limited in use due to the high price of manufacturing the various equipment including the vessels, valves, pumps, etc. required to carry out the extraction process. The source of the expense for the extraction equipment lies in the fact that such equipment must be manufactured in accordance with rigorous standards to meet the operational conditions of the extraction process such as extreme operational pressures (e.g., up to about 15,000 psi). The other source of high operational costs are associated with the energy used to perform an extraction. The first energy intensive part of the process involves a high pressure pump which must first compress the CO2 to anywhere from 800 to 15,000 psi through the extractor vessel. The resulting stream of extract saturated CO2 then de-pressurizes into a separator vessel in which the CO2 flashes to vapor thereby causing the extract to drop out into the bottom of the vessel. The vaporized CO2 must then be cooled so it returns to a liquid state before it returns to the pump inlet. These steps of pumping, compressing, depressurizing and cooling are all very energy intensive.
Moreover, CO2 acts as a refrigerant when it de-pressurizes causing extreme cooling well below 0° F. To counteract this effect, the separators must be heated in order to compensate for the cooling effect. Typically, separators must be kept at 50-60° C. to function efficiently.
Pressurizing the CO2, heating it as it cools, then cooling it when it is hot requires very high electricity usage. In certain embodiments, the present disclosure eliminates several of the pressure vessels involved in separation of extracts from CO2 and condensing CO2. It also eliminates the associated heaters and chillers in such embodiments. Pumping costs will be reduced because the circulating CO2 will remain at one steady pressure at the inlet and outlet of the pump allowing it to work less hard. Manufacturing and operational costs will be dramatically lower thereby making the technology more affordable for industry.